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3 Poisonous Plants to Avoid at Whiterock Conservancy

By: Susan Hill


Poison Ivy


How to identify: Grows in a group of three leaves, called leaflets. Leaflets may have a small “thumb” where the leaf sticks out more on one side. Stems are not hairy or thorny. Often grows into a shrub or climbs trees as vines. The size of leaflets and the plant itself can vary greatly.

  • In Spring: Leaflets red in color, with green veins, may have green flower buds

  • In Summer: Leaves darken into green, but new growth will still be red. Small white berries may be present.

  • In Fall: Leaflets turn bright red, yellow, and orange colors.

  • In Winter: Leaves will be bright red and fall off, but poison ivy is still dangerous to touch even when the leaves are wilted! Often it will not be visible under the snow.

The poison: Rash is caused by an allergic reaction to the oil urushiol. The rash does not appear until 12-24 hours after exposure, so always thoroughly wash with soap and water immediately after suspected exposure to help prevent the rash from forming. Also, urushiol can remain on surfaces such as clothing, shoes, and in pet’s fur, so be careful when handling those to prevent repeated exposure.


Warning: Never burn poison ivy! The urushiol oil becomes mobile when burned and causes very dangerous rashes to the inside of the throat when the smoke is inhaled.



Wild Parsnip


How to identify: Leaves grow alternately off the main steam and are compound (each leaf is actually many small leaflets). Each leaflet has toothed edges and is roughly egg-shaped and lobed (lobes are sections that stick out, such as the lobes on oak leaves). The stem is grooved.

  • In Spring: Wild parsnip does not bloom until June, so the plant can only be identified by its leaves and stem at this time.

  • In Summer: Easiest to identify by its tiny bright yellow flowers that grow into a flat cluster at the top of the plant (called an umbel). Flowering plants are often at least a foot tall, up to 5ft.

  • In Fall: Flowers will wilt and brown seed heads will be present. At this point, it is difficult to distinguish from plants of the same family, such as Queen Anne’s Lace.

  • In Winter: the majority of the plant dies off, but the plant easily comes back in the spring.

The poison: Parsnip causes burns, not an allergic reaction like other plants. Furanocoumarin contained in the sap of this plant causes a severe burn on the skin when exposed to sunlight, this type of reaction is called phytophotodermatitis. Simply brushing against wild parsnips is not harmful, but touching the sap from pulling parsnips or touching a broken plant will cause a painful burn. Immediately wash and cover skin from sunlight if you suspect you have touched the sap, there is no cure for parsnip burns.


Warning: Despite needing to touch an internal sap to cause burns, wild parsnip burns can cause scarring and skin sensitivity for years after the initial reaction, so avoid this plant diligently.



Stinging Nettle


How to Identify: Often found near water and growing in patches. It can grow between a few inches to 6ft high. Leaves grow opposite each other on the main stem, are very toothed, and have visible veins. The stem is hairy.

  • In Spring/Summer: Stinging nettle grows throughout the spring and summer and may bloom throughout the warm seasons. When blooming, there will be dense panicles (branching clusters) of tiny yellow-green or purple flowers coming out from the stem.

  • In Fall/Winter: Seeds will drop and plants die off during the first freezing. Plants reemerge as soon a possible in late winter/early spring.

The poison: Tiny hairs on the stem and leaves, called trichomes, inject a combo of irritating chemicals into the skin when brushed against. Stinging nettle causes a sharp stinging sensation that often fades in minutes but may feel itchy up to 24 hours after. Stronger reactions such as difficulty breathing, stomach pain, and the rash area spreading, indicate an allergic reaction and may need medical attention.


Warning: Wood nettle is another variety of nettle that has the same sting. Stinging nettle is a very common garden weed, so use gloves when pulling to avoid getting stung. Despite its sting, nettle is also commonly gathered by foragers and sometimes cultivated to make nettle teas, soups, sauces, and other recipes.



What about other poisonous plants?

Poison ivy, wild parsnip, and stinging nettle are considered the three main poisonous plants of Iowa. Other common poisonous plants, such as poison oak and sumac, do not grow in the state. All three of these plants are harmful when touched, however, the list of plants that are poisonous when ingested is far longer!



Seek medical attention if you believe you are having a severe reaction to a poisonous plant. This guide is designed to inform on identifying poison plants and their properties, and should not be used as a source of medical information or advice.



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